Daisy (Chloe Bennet) to Coulson (Clark Gregg): “Thank you for saving Simmons and I back there.”
Okay, the rule is very clear and very simple: a subject is a subject and an object is an object. And the test for whether you’re correct or not is even simpler: leave the first person out. Thus: “Thank you for saving I back there.”
Sounds like an idiot speaking!
So: Daisy should have said, “Thank you for saving Simmons and me back there.”
See? It’s easy!